Son of the noted Swedish-born Danish astronomer Svante Elis Strömgren, he early developed an interest in astronomy. He collaborated with his father on several works of astronomy and in 1940 succeeded him as director of the Royal Copenhagen Observatory.

Strömgren served as an assistant and then associate professor at the University of Chicago from 1936 to 1938 and held a variety of positions in the United States during the late 1940s. In 1951 he was appointed director of Yerkes Observatory, Williams Bay, Wis., and McDonald Observatory, Fort Davis, Texas.

It had long been supposed that luminous gas clouds in space owe their luminosity to the radiation from stars within them. Strömgren found that many of the clouds consist of ionized hydrogen surrounded by un-ionized hydrogen and that the ionized hydrogen is confined to well-defined regions.

A versatile research scientist, Strömgren worked on a wide range of astronomical problems. His determinations of the abundance of hydrogen, helium, and other elements in space differ little from presently accepted values. He did research on the internal constitution of the stars (star) and contributed to the understanding of the solar atmosphere. After 1951 he carried out an extensive program of measuring stellar spectra using photoelectric techniques. Before his efforts, the classification of stellar spectra was primarily a process of estimation.

In 1957 Strömgren joined the Institute for Advanced Study at Princeton, N.J., and 10 years later he returned to the University of Copenhagen as professor of astrophysics.